一?翻译
P5 & The signal-processing block at the transmitter conditions the source for more efficient transmission. For example, in an analog system, the signal processor may be an analog low-pass filter that is used to restrict the bandwidth of m(t). In a hybrid system, the signal processor may be an
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analogdigital converter (ADC). This produces a \word that represents samples of the analog input signal. In this case, the ADC in the signal processor is providing source coding of the input signal. In addition, the signal processor may also add parity bits to the digital word to provide channel coding so that error detection and correction can be used by the signal processor in the receiver to reduce or eliminate bit errors that are caused by noise in the channel. The signal at the output of the transmitter signal processor is a baseband signal because it has concentrated near f =0. The transmitter carrier circuit converts the processed baseband signal into a frequency band that is appropriate for the transmission medium of the channel. For example, if the channel consists of a fiber optic cable, the carrier circuits convert the baseband input to light frequencies, and the transmitted signal s(t) is light.
1 .random access memory (RAM) 2. International Telecommunications Union ( ITU ) 3.public telecommunicat/ons network ( PTN ) 4. binary-coded number 5. negative?feedback amplifer 6. adaptive equalization 7 stored-program control(SPC) 8. quadrature amplitude modulation (QAM) 9. linear integrated circuit 10. common emitter circuit 高保真度、带通信号、电磁感应、多径衰落、方框图、扩频系统、单 边带、频率配置、电离层反射、差错控制码、 二填空 P58? If the channel __ baseband signals, no carrier circuits are needed, and s⑴ can be output of the processing circuit at the transmitter. Carrier circuits are needed when the transmission channel is _ in a band of frequencies around &>>0? In this case, $(/) is said to be a because it is designed to have frequencies located in a band about&? For example, an modulated (AM) broadcasting station with an
assigned frequency of 850 kHz has a carrier frequency of j^=850 kHz. The of the baseband input information waveform m(t) into the bandpass signal s(/) is called modulation.
P23. We have seen that the op-amp^ is a high-gain direct coupled
voltage amplifier with high input impedance and low output impedance. In practice, the output voltage of an op-amp is ________ proportional to the differential voltage between its two inputs, and is equal to, VOUT=AVO(匕-V?) Where AVo is equal to open-loop voltage gain of the op-amp (typically 100, 000), Vi is the voltage at the non?inverting input, and V2 is the voltage at the inverting input.
One useful application for an op-amp is as a _____ linear amplifier in the closed-loop mode, as shown in Figure 3.4. The circuits have negative feedback applied from the output to the inverting input. That technique enables the overall gain of those circuits to be precisely
controlled by the values of the external-feedback components, regardless of the open-loop characteristics of the particular op-amps that are used. Figure 3.4(a) shows an op-amp can be used as an ___________ inverting amplifier by grounding the non-inverting terminal and feeding the input signal to the inverting terminal, or as a non?inverting amplifier by transposing the two input connections, as shown in Figure 3.4(b).It can also be used as a differential amplifier by feeding a separate input signal to each input, in which case the op-amp will amplify voltage difference between the two inputs, as shown in Figure 3.4(c). Note that if identical signals are fed to both inputs of the op-amp, ideally the output should be zero.
Figure 3.5(b) shows the circuit's transfer characteristics? Note that it is the _______ magnitude of the differential voltage at the inputs that determines the output voltage, and that the absolute values of the input voltages are of _________ little importance? For example, if a 2 volts reference is applied, a differential voltage of only 200 P V is needed to swing the output from negative saturation to positive saturation. 三?判断 P22.1n its simplest form, a conventional op-amp consists of a differential amplifier (bipolar or FFT) followed by offset compensation and output stages, as shown in Figure 3.3. All of those elements are integrated on a single chip and housed in an IC package? The differential amplifier has a
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high-impedance (constant-current)tair to give it a high input impedance and a high degree of common-mode signal rejection. It also has a high?impedance collector (or drain) load, to give it a large amount of signal-voltage gain (typically about 100 dB).
The output of the differential amplifier is fed to the circuit's output
stage via an offset-compensation network, which causes the op?amp's output to center at zero volts. The output stage takes the form of a
complementary emitter follower, and provides a low-impedance output.
Op-amps are normally powered from a split supply providing +V, -V, and a common ground, enabling the op?amp's output to swing to either side of ground and take on a value of zero volts when the differential input voltage is zero. 1 ? A conventional op?amp consists of a differential amplifier followed by current compensation and output stages. 2.The differential amplifier also has a high-impedance collector load? 3.The output of the differential amplifier is fed to the circuifs output stage via an offset-compensation network. 4. The output stage takes the form of a
complementary collector follower, and provides a low-impedance output. 5. The output stage takes the form of a complementary emitter follower, and provides a high -impedance output.
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